COPD	Chronic obstructive pulmonary disease
CTCAE	Common Terminology Criteria for Adverse Events
PICOS	Population, Intervention, Comparison, Outcomes and Study framework for systematic reviews
SMD	Standardized mean differences
OR	Odds ratio
95% CI	95 percent confidence interval
RCTs	Randomized controlled trials
Mo	Morphine
Fent	Fentanyl
HyMo	Hydromorphone
Oxy	Oxycodone
po	Per oral
sc	Subcutaneous administration
tm	Transmucosal administration
Inhal	Inhalation
SAEs	Severe adverse reactions
NS	Not specified
HTA	Arterial hypertension
RR	Respiratory rate
SaO2	Peripheral oxygen saturation
VAS	Visual analog scale for dyspnea
CPOT	Clinical pain observational tool
ECOG	Eastern Cooperative Oncology Group
NRS	Numeric rating scale
QoL	Quality of life
KPS	Karnofsky performance status
MEDD	Morphine equivalent daily dose
DOME	Daily oral morphine equivalent dose. Effective dose: Dose that reduced the intensity of dyspnea by at least 50%.
6MWT	6-min walk test
OTFC	Oral transmucosal fentanyl citrate
FBT	Fentanyl buccal tablet
FPNS	Fentanyl pectin nasal spray